Class EXTTextureSwizzle

Classic OpenGL texture formats conflate texture storage and interpretation, and assume that textures represent color. In modern applications, a
significant quantity of textures don't represent color, but rather data like shadow maps, normal maps, page tables, occlusion data, etc.. For the
latter class of data, calling the data "RGBA" is just a convenient mapping of what the data is onto the current model, but isn't an accurate reflection
of the reality of the data.

The existing texture formats provide an almost orthogonal set of data types, sizes, and number of components, but the mappings of this storage into
what the shader or fixed-function pipeline fetches is very much non-orthogonal. Previous extensions have added some of the most demanded missing
formats, but the problem has not been solved once and for all.

This extension provides a mechanism to swizzle the components of a texture before they are applied according to the texture environment in
fixed-function or as they are returned to the shader.